Data link controllers (DLCs) are used in integrated services digital networks (ISDNs) to provide a high-speed 192 kilo-bit per second (KBPS) serial interface to a telecommunications network. Various time-division multiplexed channels are employed for data transmission in ISDN, such as a signaling (D-channel) and two voice/data (B-channels). In order to provide reliable error-controlled data transmission, members of Bit-Oriented Protocol (BOP) families are used.
The ISDN protocols specify a data format that multiplexes three, 64 KBPS channels on the 192 KBPS. Furthermore, the ISDN DLC's support two independent "B" channels each having a 64 KBPS data transfer rate.